The present invention concerns a silo for the storage of lightweight hollow bodies, said silo being especially conceived (although its use can be generalized to also encompass other articles) to temporarily accumulate empty containers made of plastics material prior to ulteriorly feeding them to processing lines (filling, bottling, labelling lines, and so on), said silo being of the type that is provided with a charging inlet at a high level and at a lower region with an outlet provided to discharge the containers by gravity and arranged in a superimposed arrangement above an outfeed conveyor band connecting with a corresponding ulterior line provided for the processing or handling of said containers.
When inside a silo of big capacity (for example a right parallelepipedic enclosure with a side of 4 meters and a height of 5 meters) provided at the bottom with a discharge outlet the hollow, lightweight bodies of this kind, such as thin-walled containers made of plastics material, are highly prone to form xe2x80x9cdomesxe2x80x9d or xe2x80x9cbridgesxe2x80x9d that impede the regular and continued flow of said bodies through the corresponding discharge outlet. This is due to the fact that said bodies, for example containers, do frequently have irregular shapes and are provided with protuberances such as handles, necks, etc. causing (particularly under the conditions of random distribution and pressure of the other superimposed containers) said bodies to mutually interlock thus forming a sort of structure that is usually called a xe2x80x9cdomexe2x80x9d or xe2x80x9cbridgexe2x80x9d, said structure propping itself against the walls and thus causing a jam inside the silo thus preventing the containers involved and all those situated on top of them from descending by gravity towards the lower region of the silo.
Another limitation affecting the empty lightweight containers as regards their storage in silos of big dimensions resides in their relatively low crushing strength such as when sustaining collisions due to their free fall from an excessive height or when being submitted to the pressure exerted by the weight of a big quantity of containers piled up on top of a given container. This therefore limits the maximum height for a free fall from the upper charging inlet, as well as the maximum height for a piling up of containers inside the silo and on a bearing surface such as the bottom.
Another drawback of the above-mentioned silos, especially if they are provided for the storage of containers provided to be later on filled with liquids or beverages intended for human consumption, derives from the need to periodically clean the inside of the silo, said cleaning being a labour intensive job due to the big dimensions of these enclosures that are besides of difficult access (generally being only accessible through their top opening and through the use of lifting means or the like).
In the prior art several devices have been proposed to solve the problem of delivering by gravity other solid, compact bulk materials such as mineral coal or gravel being prone to form domes.
Documents U.S. Pat. Nos. 2,905,365 and 3,286,886 thus disclose hoppers or devices for the delivery of bulk materials which are both formed by a bin with rigid, flat, fixed walls and with a rectangular cross-section whose surface area tapers from top to bottom, said bin being provided with an outlet at its lower end. Innerly attached to at least one of said walls is a rigid flat plate connected to means provided to impart a vibratory motion to said plate.
This arrangement has the drawback that between the rigid plate and the hopper""s wall a gap is formed which tends to receive and accumulate dirt particles that hinder the operation of the device and whose removal without disassembling the unit involves a difficult cleaning operation. On the other hand, since the mechanisms provided to transmit the vibratory motion are arranged outside the hopper they must pass through the corresponding fixed wall of the latter in order to connect with the movable plate, this entailing a relative complexity of said mechanisms.
Document WO 95/03233 does moreover disclose a hopper for the delivery of bulk materials consisting in a bin of frustoconical shape whose cross-sectional surface area tapers from top to bottom, said bin being provided with an outlet at a lower end. The wall of said bin is formed by at least a rigid, fixed portion and at least a rigid, movable portion connected to means provided to generate a vibratory motion. This arrangement, although representing a certain simplification of the mechanisms as compared with those mentioned above, has the drawback that the element to be vibrated is at least a substantial portion of the main wall of the bin and has to be strong enough to withstand the pressure exerted by the material, said portion of said wall therefore having a relatively big mass and thus entailing a high energy consumption.
The devices described in the three above-mentioned documents are useful for the delivery of solid, compact bulk materials such as for example mineral coal, gravel, etc. which are not to be damaged by blows or as a result of being crushed. Such devices are nevertheless not apt to deliver in bulk lightweight hollow bodies such as containers made of plastics material, since these latter are liable to be crushed by the vibratory motion of the rigid plates or rigid portions of the bin in combination with the decreasing cross-sectional surface area of the latter, as well as by the weight of the very hollow bodies piled up on top of each other inside the silo, especially if this latter has a considerable height.
Also known in the art are devices such as deflector plates, nets with passage openings big enough for the containers, or labyrinths situated at different levels inside a tall silo, said devices being provided to limit the maximum height for a free fall of a container upon another one situated at a lower level, and the maximum height for the piling up of containers on top of a specific container in particular. Said deflector plates, nets or labyrinths are nevertheless a hindrance for the free flow of the stored articles, this then having to be added to the problem of the formation of xe2x80x9cdomesxe2x80x9d or xe2x80x9cbridgesxe2x80x9d.
Other technical background of interest regarding the object of the invention is to be found in patents U.S. Pat. No. 5,687,881 and WO-A-96/30727, EP-A-033 815, EP-A-001576, EP-A-0336815 and U.S. Pat. No. 4,127,970.
The invention provides a silo of big capacity for the temporary storage of lightweight hollow bodies, said silo being provided to be emptied by gravity and being especially apt to accumulate said containers for example coming from a container production area prior to an ulterior delivery when the necessity arises to continuously feed empty plastic containers for example to bottling lines where said containers will be submitted to different processing operations (filling, capping, labelling, etc.). It thus becomes feasible to adapt the production of the machines forming said containers, for example injection moulders, to the needs of the bottling lines during the operational cycles of these latter.
According to a first object of this invention said silo is provided with means to adjust inclines delimiting the bottom of the silo or to jolt or vibrate said bottom in order to prevent the formation of xe2x80x9cdomesxe2x80x9d or xe2x80x9cbridgesxe2x80x9d or to disrupt them, as the case might be.
Another object of the invention consists in a dispensing device adapted to deliver empty plastic containers to a conveyor belt with a regular and controlled flow of said containers and with the possibility of an adaptation to the characteristics of size and shape of said containers.
Another object of this invention is that of providing a silo apt for the storage of lightweight hollow bodies, especially empty plastic bottles, the walls of said silo being easily washable since they can be xe2x80x9ctransferredxe2x80x9d to the outside thus allowing to easily have access to all parts of their surface.
Yet another object of the instant invention is that of providing a silo for the controlled storage and delivery of empty lightweight containers, said silo being provided with means to limit the maximum height for a free fall of a container upon another container situated at a lower level, and the maximum height for the piling up of containers on top of a specific container in particular inside the silo.
Finally another object of the present invention is that of providing a method for the controlled storage and delivery of empty lightweight containers by means of a silo provided with the means mentioned in the two paragraphs above.
According to an exemplary embodiment of the present invention related with the last mentioned object a silo is provided for the controlled storage and delivery of empty lightweight containers, said silo being of the type that comprises an amply dimensioned bin provided with a charging inlet at its upper region and with a bottom with at least a controllable discharge outlet at its lower region, said bin being filled and emptied by gravity. In order to limit the maximum height for a free fall of a container upon another container situated at a lower level, as well as the maximum height for the piling up of containers on top of a specific container in particular, said silo comprises a division of said bin into mutually superimposed enclosures that are apt to be filled by gravity and whose height is a function of the type of container to be stored, said enclosures being delimited by retractable supporting floors provided with independent driving means apt to shift them in order to thus open or close at least a passage therethrough for the discharge of containers from an enclosure into the next lower enclosure.
In a preferred exemplary embodiment said supporting floor comprises at least a flexible sheet such as a canvas apt to be wound up around a rotary reel supported next to one of the lateral walls of said bin, a frontal free edge of said flexible sheet being attached to a loadbearing bar apt to be shifted away from and towards said rotary reel thereby being supported and guided along a predetermined track formed, for example, by a pair of lateral rails supporting corresponding wheels or runners fitted to both ends of said loadbearing bar. Said predetermined track, being preferably horizontal, comprises retractable stops that prevent the loadbearing bar from being shifted backwards when the flexible sheet is in the extended condition.
The loadbearing bar is provided with pushing means comprising a pair of articulated arms each of which is formed by two sections that are linked to each other, each arm being linked at an end to the framing, at a location near the rotary reel, and at the other end to the loadbearing bar, each of said arms including an extension spring attached at one end to one of said sections and connected by means of a flexible element to the other of said sections thus imparting to said sections a tendency to spread up and to thus adopt a mutually aligned position thus pushing said loadbearing bar away from said rotary reel. An electric motor drives said rotary reel in favour of or against said pushing means to respectively extend and withdraw said flexible sheet.
The silo of the present invention does optionally comprise lateral walls formed by linens of flexible sheet provided with reinforced peripheral edges and attached to a supporting frame by means of stretchers distributed along said edges. By way of stiffeners for said lateral walls extended cables are arranged across the outer surface of said linens and are attached by means of tighteners to said supporting frame.
In order to facilitate the manufacture, transportation and assembly of said silo taking into account its big dimensions, each of said supporting floors is associated to a portion of the framework of said bin thus forming a modular assembly apt to be fitted in a stacked arrangement on top of a base module to thus form a bin of a desired height, said base module including said bottom and discharge outlet, said modular assemblies being attached to each other and to the base module at the final location by means of detachable or permanent connections.
Irrespective of the type of embodiment chosen for the supporting floors, in the silo as per the present invention detecting means have been besides provided to detect the level of containers having accumulated on the supporting floor and/or on the bottom. In response to signals received from said detecting means control means are apt to act on at least said supporting floor driving means so as to control the flow of containers from one enclosure into another and the maximum quantities of said containers in each enclosure. Said control means are optionally integrated into a general control system governing the feeding into said silo and the controlled delivery of containers from this latter onto, for example, a packaging line.
The precited silo is operated by following the method for the controlled storage and delivery of empty lightweight containers hereinafter described, said method also being an object of the present invention.
With a silo such as that described above whose bin is divided into mutually superimposed enclosures by means of retractable supporting floors, said enclosures being upperly filled by gravity, said supporting floors,being provided with independent means apt to at a desired point in time selectively communicate with each other two of the aforesaid enclosures, and the height of said enclosures being adapted to the minimum value of the maximum free fall height or the maximum heaping up height a predetermined type of container can withstand with no damage, said method is characterized in that:
when starting to feed said bin this is always done by means of first charging the highest enclosure, and with this latter isolated from the next following one;
any enclosure is always discharged by means of communicating it with the next lower enclosure, with this latter being at least in part empty as well as isolated with respect to the next following one, except when the next lower enclosure is that situated at the lowest level and inferiorly delimited by said bottom and said controllable discharge outlet, in which case said discharge outlet can be:
closed, in order to store containers; or
open up to a selected extent for a controlled delivery of said containers.